m-Azido-phencyclidine covalently labels the rat brain PCP receptor, a putative K channel.

Phencyclidine (PCP) binds with high affinity to a specific receptor in rat brain membranes, which is likely a voltage-gated, noninactivating potassium channel. Several potassium channel blockers, including aminopyridines and tetraalkylamines, displace PCP from this binding site, supporting the hypothesis. A photolabile PCP analog, m-azido-PCP, binds reversibly to two classes of sites on rat brain synaptic membranes: a high-affinity site (dissociation constant 0.14 ± 0.01 µM) and a low-affinity site (255 ± 55 µM). The high-affinity site corresponds to the PCP receptor. The rank order of potency for displacing PCP from this site among aminopyridines is 4-AP ≈ 3,4-diAP > 2-AP ≫ 3-AP; among tetraalkylamines it is TBA > TEA ≫ TMA.

Study at a glance

Abstract

Phencyclidine (PCP) is a schizophrenomimetic drug of abuse. PCP binds with high affinity (apparent dissociation constant, KD less than 10(-6) M) to rat brain membranes and blocks, selectively, a voltage-gated, noninactivating K channel found in rat brain synaptosomes (presynaptic nerve terminals). Thus, it has been proposed that the high-affinity PCP receptor in brain is this K channel. Consistent with this hypothesis, we now show that several K channel blockers displace 3H-PCP from the rat brain receptor. Additionally, we have used a photolabile analog of PCP, m-azido-PCP (Az-PCP), to identify the brain PCP receptor/putative K channel. In the dark, Az-PCP bound reversibly to 2 classes of sites on rat brain synaptic membranes [KD = 0.14 +/- 0.01 microM (n = 5) for high-affinity binding, and KD = 255 +/- 55 microM for low-affinity binding]. Competitive binding studies between Az-3H-PCP and nonlabeled PCP analogs, and between Az-PCP and several tritiated PCP analogs, indicated that the high-affinity Az-PCP binding site is the high-affinity PCP receptor. Several amino-pyridines (APs) and tetraalkylamines (TAAs), which are known to block K channels in excitable cells, were also found to displace 3H-PCP from its high-affinity binding site on rat brain synaptic membranes. The rank order of potency for displacement of 3H-PCP from this site for the APs was 4-AP approximately equal to 3,4-diAP greater than 2-AP much greater than 3-AP; for the TAAs it was TBA greater than TEA much greater than TMA (the tetra-butyl, ethyl, and methyl amines, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)